基于小波变换和动态聚类的图象分割方法

本文讨论了一种结合小波变换和非监督动态聚类的图象分割算法。在图象分割过程中,首先用小波变换提取图象中的边缘信息,再利用所得的边缘信息和原图象的灰度信息进行聚类。实验证明了这种方法是行之有效的。     

厚壁不锈钢管受压柱单侧出现塑性时的稳定分析

根据压弯构件的极限强度理论,对厚壁不锈钢管受压柱单侧出现塑性时的稳定承载力进行了分析,得出了它的稳定系数公式,并指出其应用条件。     

自蔓延离心法制备不锈钢内衬复合钢管的显微结构

用扫描电镜和透射电镜研究了自蔓延离心法制备的不锈钢内衬,（Ｃｒ,Ｎｉ分别为１３％～１４％和１４％－１６％）复合钢管不锈钢层的结晶特点和组织结构,研究表明,不锈钢熔体主要以柱状晶形式结晶,柱状晶由奥氏体组成,柱状晶间有一薄层铁素体,铁素体区有ＡｌＮｉ金属间化合物析出相,在奥氏体和铁素体相界的铁素体区一侧有σ相析出。     

选区激光熔化快速成型过程分析

分析了选区激光熔化的成型过程及成型机理,归纳了该工艺的技术特征,推导了温升与加工参数间的解析关系式,并据此优化了选区激光熔化快速成型的工艺.采用Cu-P合金对成型工艺进行了实验验证,分析了扫描速度及激光功率对成型质量的影响,探讨了球化的成因及消除方法.结果表明,通过合理配置扫描速度、扫描间距、激光功率等加工参数,可以直接成型具有高致密性的金属零件.     

Copula-based risk management models for multivariable RMB exchange rate in the process of RMB internationalization

This paper investigates the dependence of the exchange rate of onshore Renminbi (RMB) and offshore RMB against US dollar (i.e., CNY and CNH) based on copula models. Eleven different copulas were selected to construct multivariate distribution and estimate the value-at-risk for RMB exchange rate. Empirical results show that time-invariant Student-t copula is the best model to fit the sample data. The positive upper and lower dependence indicates that CNY and CNH series tend to move in the same direction. Moreover, the dependence between the two exchange rates is asymmetric, which means that traditional models, such as Pearson’s correlation, are inappropriate to measure the correlations between these markets. The best fitted model is chosen to estimate the financial risk, which can help business practitioners and policymakers track risk evolution and make good decisions.     

储能产业发展带来的能源革命及其关键管理科学问题

储能产业的爆发式增长,不是一个独立的产业现象,而是以新能源利用为主要导向的能源生产和能源消费革命的必然要求,会导致能源供给和消费的系统性变革.在这个系统变革中,有很多管理科学的问题亟待学术界的关注和研究.讨论了多个包含储能发展的实际应用场景,针对共享储能的集中式储能和产销一体化的分布式储能等新兴发展的储能模式,从可行性...     

特高含水后期矢量开发调整技术研究及应用

针对胜利油区整装油田特高含水后期油藏开发面临层间干扰严重、井网不完善、驱替不均衡的问题,基于油藏工程理论和数理优化方法,攻关研究整装油田矢量开发调整提高采收率技术,建立了一级层间矢量层系重组、二级平面矢量井网重整到三级注采优化调整的矢量开发调整技术。该技术具备井网形式灵活、老井利用率高、投资成本低的特点。应用实例表明,该技术控水稳油、降本增效作用明显,有利于实现特高含水后期油田进一步提高采收率。     

车辆荷载下综合管廊应力响应及疲劳损伤分析

作为一种浅埋隧道,综合管廊不可避免会受到车辆荷载的影响。为保证管廊结构运营期安全,有必要研究循环动荷载对管廊结构的影响。依托某综合管廊工程,使用ANSYS建立管廊-车辆荷载三维模型,研究了综合管廊在不同车辆荷载条件下的应力响应,发现在车辆荷载一个作用周期内,管廊的主拉应力时程曲线可分为上升区、峰值区及下降区;各车辆工况下管廊上部应力变化幅度在10%~15%左右,下部应力变化幅度在1%左右,距离地表越远的部位应力变化幅度越小。在得到管廊应力时程数据后,基于3种不同的疲劳公式编写程序对管廊进行疲劳分析,发现按Cornelissen公式及吕培印公式计算,管廊结构的最低使用寿命分别为0.42年及24.8年,不满足其设计使用年限,因此有必要考虑管廊在车辆荷载下的疲劳效应;其中管廊疲劳损伤主要集中在管廊的5个部位,中舱顶板、两中隔墙的顶端和底端,其中中舱顶板所受疲劳损伤最大,这5个部位应是综合管廊结构设计以及运营期间应重点关注的部位。     

Genome-wide genetic changes during modern breeding of maize

The success of modern maize breeding has been demonstrated by remarkable increases in productivity over the last four decades. However, the underlying genetic changes correlated with these gains remain largely unknown. We report here the sequencing of 278 temperate maize inbred lines from different stages of breeding history, including deep resequencing of 4 lines with known pedigree information. The results show that modern breeding has introduced highly dynamic genetic changes into the maize genome. Artificial selection has affected thousands of targets, including genes and non-genic regions, leading to a reduction in nucleotide diversity and an increase in the proportion of rare alleles. Genetic changes during breeding happen rapidly, with extensive variation (SNPs, indels and copy-number variants (CNVs)) occurring, even within identity-by-descent regions. Our genome-wide assessment of genetic changes during modern maize breeding provides new strategies as well as practical targets for future crop breeding and biotechnology.